1. Field of the Invention
The present invention relates to a method for fabricating a single-crystal semiconductor.
2. Description of Related Art
Semiconductor devices are generally formed on a high-purity single-crystal silicon wafer which is, in general, fabricated by Czochralski (CZ) method. The CZ method charges polysilicon blocks in a crucible inside a single-crystal fabricating apparatus and melts the blocks by heaters around the crucible. A seed which is held by a seed holder is then immersed in the melt and lifted with rotating in clockwise or counter-clockwise direction to grow the single-crystal silicon.
The process for fabricating the single-crystal semiconductor by means of the CZ method includes four steps as follows.
1. Necking step: a slender crystal region is grown to prevent the propagation of dislocations of seed crystal.
2. Crown step: a crystal region without dislocation is grown with its diameter gradually expanded to a predetermined dimension.
3. Body step: a crystal body having a diameter of the predetermined dimension is grown.
4. Tail step: in order to prevent the propagation of dislocation in the crystal body due to inconsistent thermal processes, a crystal region having a diameter which is gradually decreased is grown, thereby separating the crystal region from the melt.
The tail step requires about 10% of the total cycle time. Since the tail region cannot be utilized as a product, the time required in the tail step should be as short as possible. However, since the tail step is provided for eliminating the dislocation, it cannot be omitted. Therefore, the tail step is critical to the reduction of the cycle time for fabricating the single-crystal semiconductor.